Understanding
Isometric-Isotonic Contractions

Many people are confused about isometric-isotonic
contractions. What exactly are the differences between the two
contractions and what are the advantages and disadvantages of each?

Isotonic Contractions

Exercises which utilize isotonic
contractions are typically the
exercises that everyone is aware off. Swinging a bat, throwing a ball
or lifting a weight are all isotonic movements. Most of the bodyweight
exercises in "Natural Fitness" and "Animal Workouts", not to mention "Power
Isotonics", are Isotonic in
nature as well. Anatomy wise, an isotonic movement is one in which a
muscle is shortened and the body part it is attached to moves as well.
If you perform a bicep curl, the process of shortening the bicep is
what moves the arm.

Isometric Contractions

Isometric Contractions, on the other hand, are situations where the
muscle TRIES to contract, but cannot. An example of this is if you
tried to lift an immoveable object. Holding a weight at arm's length
would be another. Actually, the legendary Bruce Lee, who was famous for
his isometric workouts, did an exercise like this. He would hold a 3
pound steel ball in front of him with a straight arm for as long as he
could. When he couldn't stand it anymore, he would drop the weight into
the opposite hand and repeat the movement. He would alternate back and
forth like this for 8 hours. This is obviously an extreme example, but
that's also why the Dragon was the Dragon.

Isotonic Benefits

Exercises based on Isometric-Isotonic
contractions have their
benefits. However, Isotonic movements typically are much more vigorous,
which is better for the heart. Isometrics only work the heart
indirectly. Due to their vigorous nature, isotonic exercises
are usually better at burning calories and therefore greatly aid in
weight reduction. Most people don't realize that if you eat an extra
100 calories a day, that can add up to 10 pounds a year. Walking for an
hour (an isotonic exercise) will burn this off.

Isometric Benefits

The primary benefit of isometric contractions is that they work muscle
fibers that would otherwise remain idle. They are able to do this as
isometric exercises (when done properly) force ALL of the muscle fibers
to become fatigued. In weightlifting terms, they "allow you to get to
the last rep first." They also take less time to perform that isotonic
exercises and may also do a more efficient job of building and toning
muscles. They are also safer can be done anywhere, which makes them
more convenient.

Conclusions

Isometric-Isotonic contractions have their benefits. In
the end, you will have to decide what your fitness goals are to
determine which one is best for you. In
my opinion, a balanced exercise program should contain both
contractions, which is what I do.